The present invention relates to a device for determining the physical characteristics of a fluid comprising a vapor phase, such as its liquid-vapor equilibrium pressure.
Knowing the liquid-vapor equilibrium of fluid mixtures is of great importance in certain techniques, such as in operations of separation by distillation and adsorption, in the exploitation of oil or natural gas deposits, in techniques of refrigeration or production of thermal energy by heat pumps which make use of liquid vaporization or vapor absorption in a suitable solvent under determined temperature and pressure conditions.
It is possible to carry out measurements on a fluid by placing it in a chamber where it can be compressed.
To obtain a sufficient accuracy in the preformed measurements, it is however necessary to solve the difficult problems of introduction of the fluid under study into the chamber and of temperature regulation, with the additional problem of compatability between the fluid under study, and mercury when the latter is used to apply compression to the fluid.
An apparatus for measuring vapor pressure is described in French Pat. No. 1,396,489.
However, this apparatus permits neither stirring and weighing of the sample, nor accurate determinations of its composition.
Furthermore, it suffers from the drawback of leaving an large dead volume around the bellow and does not permit uniform thermoregulation.
British Pat. No. 974,103 describes an apparatus for measuring quantities of dissolved gas, which is not suitable for accurately determining liquid molar fractions.
The shape of the cell of this apparatus is moreover, complex and makes thermoregulation difficult. This British patent does not make provision for accurate measurement of liquid densities.
Furthermore, this prior art device requires the use of models for processing data relating to pressure values.
The publication of GIBBS and VAN NESS in Industrial and Engineering Chemistry Fundamentals (11,410,1972) describes an apparatus of constant volume which can only be used for liquid-vapor equilibrium measurements. The molar fractions in liquid phase are, however, derived from a model and not from direct sample weighing. It is difficult to estimate the vaporized fraction particularly at high pressures (the results given by the authors are relative to pressures lower than one atmosphere). The introduction of the compounds under study is effected by means of volumetric pumps, and requires knowledge of the fluid density at the inlet pressure, in order to determine the fluid masses introduced into the cell.